The present invention relates to a semiconductor integrated device with a high tolerance against abnormally high input voltages, and more particularly to a metal-insulator semiconductor integrated device having such a tolerance.
Metal-insulator semiconductor devices have advantages over bipolar semiconductor devices in a lower number of manufacturing steps, in a smaller area required for each element, in a narrower isolation region between adjacent elements, etc. Because of these advantages, metal-insulator semiconductor devices are useful for integrated circuits of, for example, memory circuits or logic circuits. In order to achieve a high speed operation of these integrated circuits, technical attempts have been made to minimize the metal-insulator semiconductor device by more and more decreasing the size of each element in the device, or by forming a shallow surface layer. Such attempts have reached a high integration degree. However, the miniaturization of the integrated device has been causing a problem, namely the lowering of the tolerance voltage against abnormally high input voltages. Such an abnormal voltage occurs due to, for example, static electricity produced by friction of the input pins of the device with other materials. While the tolerance voltage is up to several tens of volts, the abnormal voltage due to static electricity reaches more than several thousand volts. Therefore, the minimized integrated device is easily destroyed by such an abnormal voltage.